There are a number of drug compositions commercially available for the treatment of disease. These drugs are most commonly delivered as an oral dosage form (e.g. as a pill, capsule, or tablet), or delivered intravenously. Disadvantages of oral dosage forms include a delay in the onset of activity and loss of drug therapeutic effect due to hepatic first-pass metabolism. Intravenous delivery, while typically more effective than oral delivery, is often painful and inconvenient. Thus other dosage forms and routes of administration with improved properties are desirable.
One such alternative is inhalation therapy. Many preclinical and clinical studies with inhaled compounds have demonstrated that efficacy can be achieved both within the lungs and systemically. Moreover, there are many advantages associated with pulmonary delivery including rapid onset, the convenience of patient self-administration, the potential for reduced drug side-effects, ease of delivery by inhalation, the elimination of needles, and the like. Yet, in spite of these advantages, pulmonary delivery through inhalation therapy has played a relatively minor role in the administration of therapeutic agents when compared to more traditional drug administration routes of oral delivery and delivery via injection.
The role of inhalation therapy in the health care field has remained limited mainly to treatment of asthma, in part due to a set of problems unique to the development of inhalable drug formulations, especially formulations for systemic delivery by inhalation. Inhalation aerosols from dry powder inhalers, nebulizers, and pressurized metered dose inhalers typically include excipients or solvents to increase stability or deliverability of these drugs in an aerosol form. Additionally, control of the particle size of these drug aerosols is challenging and depends on the method used to form the aerosol and the other excipients added.
For example, when using dry powder inhalers (DPI's), the need to mill the drug to obtain an acceptable particle size for delivery to the lungs is problematic. Some mills used for micronization are known to produce heat, which can cause degradation of the drug if prolonged, and tend to shed metallic particles as contaminants. Moreover, as dry powder formulations are prone to aggregation and low flowability which can result in diminished efficiency, scrupulous attention is required during milling, blending, powder flow, filling and even administration to ensure that the dry powder aerosols are reliably delivered and have the proper particle size distribution for delivery to the lungs.
Nebulizers generate an aerosol from a liquid, some by breakup of a liquid jet and some by ultrasonic vibration of the liquid with or without a nozzle. All liquid aerosol devices must overcome the problems associated with formulation of the compound into a stable liquid state. Liquid formulations must be prepared and stored under aseptic or sterile conditions since they can harbor microorganisms. This necessitates the use of preservatives or unit dose packaging. Additionally solvents, detergents and other agents are used to stabilize the drug formulation.
Pressurized metered dose inhalers, or pMDIs, are an additional class of aerosol dispensing devices. pMDI's package the compound in a canister under pressure with a solvent and propellant mixture, usually chlorofluorocarbons (CFC's,), or hydrofluoroalkanes (HFA's). Upon being dispensed a jet of the mixture is ejected through a valve and nozzle and the propellant “flashes off” leaving an aerosol of the compound. With pMDI's particle size is hard to control and has poor reproducibility leading to uneven and unpredictable bioavailability. Moreover, due to the high speed ejection of the aerosol from the nozzle, pMDIs deliver drug inefficiently as much of the drug impacts ballistically on the tongue, mouth and throat and never gets to the lung.
Thus, there remains a need for methods to prepare aerosols that are readily deliverable and have minimal formulation issues. One such method is to deliver drugs via vaporatization.
When using vaporization to form an aerosol, controlling a compound's degradation and anticipating the energies which activate thermal degradation are typically very difficult. Activation energies of these reactions depend on molecular structures, energy transfer mechanisms, transitory configurations of the reacting molecular complexes, and the effects of neighboring molecules. Thus, while vaporization followed by condensation of the vapor to form an aerosol provides a possible mechanism to eliminate the need for costly formulations, which include excipients and other materials that are likely to change the pharmcokinetics and bioavailability of a drug, the challenge of using this technique for generating drug aerosols resides in the ability to control thermal degradation during the vaporization step.
The present invention overcomes the foregoing discussed disadvantages and problems with other inhalation technologies and provides a mechanism to control thermal degradation during vaporization making it possible to produce pure aerosols of organic compounds without the need for excipients or other additives, including solvents, wherein the particle size is stable and selectable.